In tufting machines, it is desirable to provide a driving mechanism that permits the tufting machine to operate at relatively high speeds and that also is adjustable to permit tufting of varying lengths of yarn through backing material. Typically, the variation in tufting is accomplished by altering the stroke of the needle bar as with the use of cams of varying eccentricity that cooperate with connecting rods to reciprocate the needle bar. It is particularly desirable to able to change the length of the needle stroke of tufting machines without the necessity for removing the entire drive shaft of the machine. Furthermore, when operating the tufting machine at high speeds, any forces acting on the tufting machine that are not properly counterbalanced tend to set up a vibration in the tufting machine. At typical high speed operation involving 1500 to 1800 stitches per minute, even small issues of imbalance may create vibrations which will damage the tufting machine or its mountings.
In tufting machines, one or more rows of yarn carrying needles are reciprocally driven through a backing material fed through the machine across a bed plate to form loops that are seized by loopers oscillating below the backing material and bed plate in timed relationship with the needles. To change the depth of pile height produced by a tufting machine, it is necessary to change the length of the stroke of the needles, and the elevation of the bed plate relative to the loopers, as is well known in the prior art and described in U.S. Pat. No. 2,977,905. The actual bottom point of the stroke of the needles must remain constant so that the loopers and needles retain their proper relationship. Otherwise, the loopers will not properly seize the loops of yarn from the needles. To maintain this relationship a variety of methods have been utilized including using interchangeable push rods or connecting rods of varying lengths; using shims; or using adjustable length push rods or connecting rods. In order to properly maintain the relationship between the needles and loopers, changes to the length of the needle stroke as well as the attendant adjustments are generally performed with the tufting machine stopped at bottom dead center of the needle stroke.
Changing the stroke in high speed tufting machines has previously been accomplished by three general constructions. In one construction, the eccentrics are adjustable. The most widely used adjustable eccentrics involve two non-adjustable hubs which can be clamped tightly against the eccentric. When the hubs are loosened, the eccentric can be adjusted to alter its throw. Other types of adjustable eccentrics have generally either involved too many parts and adjustments to make changes in stroke length quickly and correctly, or have lacked the structural stability required to withstand the radial forces of driving the connecting rod and needle assembly at high speeds. Examples of such adjustable eccentrics are illustrated in U.S. Pat. Nos. 3,857,345 and 4,515,096. In a second type of general type of construction, two or three eccentrics of different throws are mounted on the rotating shaft adjacent to each connecting rod. To adjust the stroke, the eccentric strap is loosened and the eccentric with the desired throw is engaged. This leaves unused eccentrics mounted on the rotating shaft. In a third construction, split eccentrics are joined about the rotating shaft and can be disassembled and replaced with alternate eccentrics of a different throw when desired, as described in U.S. Pat. No. 5,320,053.
An alternative to these types of construction permitting adjustable throw length from a main drive shaft is the utilization of stub shafts with belt or chain drive connections to the main drive shaft. In this type of assembly, a main drive shaft is mounted with several sheaves across its length, and these sheaves engage by belt or chain with sheaves on associated stub shafts on which eccentrics may be mounted. Thus, when it is desired to change the throw of the tufting machine, it is not necessary to pull the main drive shaft, but only the stub shafts. Various assemblies of this nature are described in U.S. Pat. Nos. 4,665,845; 5,572,939; 5,706,745 and 5,857,422.
Whenever the throw or stroke of the tufting machine is changed, slight variations in balance and counterbalance are introduced. Furthermore, tufting machines may be operated at different speeds due to the change in the length of the stroke of the needles. Generally longer strokes entail slower speeds than shorter strokes and the variation in stroke and speed affects the vibratory characteristics of the tufting machine. Indeed, changing either the length of the stroke or the speed of operation of the tufting machine alone may alter the vibratory characteristics of the machine. It is often desirable to change the speed of operation to slower speeds when tufting patterns with lateral needle bar shifts, particularly shifts of multiple gauge units. It may also be desirable to operate at slower speeds when tufting with bulky yarns relative to tufting with smooth, narrow yarns. Each yarn and pattern combination may have a speed that is a “sweet spot” for optimal tufting performance that minimizes the number of yarns dropped from loopers. Therefore, it is necessary to minimize tufting machine vibrations over a range of throw lengths and operating speeds.
The counter balancing weights heretofore used to minimize vibration in tufting machines have principally been located either on the main drive shaft or on a shaft driven in synchronization from the main drive shaft or main drive motors. Often these counter balancing mechanisms are not adjustable over changes in length of stroke or speed of tufting machine operation. When counter balancing mechanisms have been adjustable, the adjustments are cumbersome, frequently requiring opening the tufting machine head and always requiring the tufting machine to be stopped.
What is needed therefore is an improved mechanism to reduce vibration in tufting machines that is easily adjustable over a range of throw lengths and speeds of tufting machine operation. According to the invention, a shaker driven by a servo motor independent of the main drive motor is utilized to rotate a counter balancing weight to act in opposition to the vibration of the tufting machine.